Abstract
Although several graphs have been published illustrating the post-natal growth of the human brain, as well as a few of the growth of the major divisions of the structure, apparently no attempt has been made to analyze these curves and to develop formulæ for the expression of the relation between brain weight and age between birth and maturity. We have made a series of calculations of this type and have computed empirical formulæ for the growth of the encephalon as a whole, the cerebrum, the cerebellum, and the pons, medulla and mid brain, from birth to 20 years. These formulæ have been determined from the weighted average of male and female brain weights. While it will no doubt be possible to develop slight varients of these formulæ for the weight of the entire brain and of the cerebrum for males and females separately, our data indicate that it is hardly practicable to establish separate curves for the sexes, on the basis of the material now available, for the weight of the cerebellum and the brain stem. Likewise no attempt has been made to correct graphically or mathematically for the effect of disease on the weight of the brain although all records of cases involving any brain pathology were rigidly excluded. The curves and formulæ, therefore, represent the growth of the organ in a hospital rather than in the general population.
When plotted against age and tested graphically all the curves of the postnatal growth of the brain approach hyperbolae and may be expressed approximately by the general formulae:
In these formulae, Y is the weight of the brain or brain-part, X is the age in years and a, b and c are empirically determined constants.
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